An oil-gas well generally refers to a production well in the oil-gas field development in a broad sense, including an oil well, a gas well, an injection well and so on. In the production process of the oil-gas well, due to the heterogeneous characteristic of the oil reservoir, the oil-gas well, regardless of a vertical well or a horizontal well, has to be sealed off and separated into multiple independent zones for production. The oil-gas well production mentioned herein includes the production and injection of the fluid in the oil-gas well production process, for example, injecting water and vapor into the formation in the petroleum exploitation or production process, and injecting chemical agents for improving the oil field recovery ratio, and also includes the injection of acid liquor into the formation in some operation processes, etc.
During the process of sealing off and separating the oil-gas well into multiple independent zones for production, a device for controlling flow rate in sections (for example, a flow control filter string), and a device for separating the production section of the oil-gas well into several flow units along the axial direction of the oil-gas well (for example, a packer) are generally used to realize the seal and separation of the zones, so as to realize relatively independent production.
FIG. 1 is a schematic view illustrating the flow control by using a flow control filter string and a packer in an open hole. In FIG. 1, reference numeral 1 indicates a borehole wall of the oil-gas well, reference numeral 2 indicates a flow control filter string, reference numeral 3 indicates an annular space between the flow control filter string and the borehole wall, reference numeral 4 indicates a packer hung with the flow control filter string, and reference numeral 5 indicates a flow control packer.
The process of sectional flow control is briefly described hereinafter with reference to FIG. 1. FIG. 1 shows a non-oil-bearing formation, an oil-bearing formation and bottom water under the oil-bearing formation. Various formations are schematically indicated by horizontal lines in FIG. 1, though the person skilled in the art may understand that these formations may not be horizontal, which depends on the geologic structure of the locality where the oil-gas well is located. The oil-gas well as shown in the figure includes a vertical section and a horizontal section. The horizontal section substantially extends along the oil-bearing formation so as to increase the contact area between the borehole wall and the oil-bearing formation. FIG. 1 illustratively shows two zones having different permeability, i.e. a high permeability zone and a low permeability zone. Under the situation without flow control in the oil-gas well (i.e. no packer 5 is provided in FIG. 1), since the permeability of the two zones is different, a flow rate of the fluid in the high permeability zone is larger than a flow rate of the fluid in the low permeability zone. In this case, due to the difference between the pressure of the bottom water and the pressure inside the oil-gas well, the bottom water under the oil-bearing formation may firstly pass through the high permeability zone and enter into the oil-gas well, which may cause the decrease of oil and gas and the increase of water in the production of the oil-gas well. This should be avoided in the production.
Currently, as shown in FIG. 1, the sectional flow-rate control production in many oil-gas wells is realized as follows. A flow control filter string 2 is lowered into the production section inside the oil-gas well, and the flow control filter string 2 and the packer 5 are used to effectively seal off and partition an annular space between the flow control filter string 2 and the production section inside the oil-gas well, i.e. axial channeling passage of fluid outside the flow control filter string is blocked, thereby realizing a better sectional flow-rate control production. Generally, the packer is provided between two zones having different permeability. Since the flow control filter can play a role of flow-rate control, the packer is used to pack off the zones having different permeability so as to perform independent control or sectional control of various zones having different permeability. Therefore, it is possible for the oil-gas well to achieve a good production, and to effectively control the quantity of the bottom water entering into the oil-gas well.
However, the current well completion of the oil-gas well is achieved by running a perforated pipe into an open hole, and an annular space between the perforated pipe and the open hole wall is not sealed by filling cement or other materials between the perforated pipe and the borehole wall. The well completion method has an advantage of the low cost, and a disadvantage that the annular space becomes a passage for fluid channeling, so that it is difficult to realize the sectional flow control in the later production. Each meter of the perforated pipe is provided with several to dozens of holes with a diameter about 10 mm. The perforated pipe is mainly used in the oil-gas well to support the borehole wall and prevent lumps in the well from entering into the perforated pipe so as to ensure that the whole flow passage of the oil-gas well is not blocked by lumps.
As shown in FIG. 2, if the flow control technology using the packer in the open hole as shown in FIG. 1 is directly applied in the existing oil-gas well having the perforated pipe, the annular space between the perforated pipe and the borehole wall cannot be packed off. Thus, the bottom water entering into the oil-gas well may flow axially in the annular space between the perforated pipe and the borehole wall. Thus, the annular space between the perforated pipe and the borehole wall forms an axial channeling passage, which destroys the pack-off effect between the flow control filter string in the perforated pipe and the perforated pipe, and cannot control the amount of water satisfactorily. In FIG. 2, reference numeral 11 indicates a borehole wall of the oil-gas well, reference numeral 12 indicates a perforated pipe, reference numeral 13 indicates an annular space between the perforated pipe and the borehole wall, reference numeral 14 indicates a packer hung with the perforated pipe, reference numeral 15 indicates a flow control filter string, reference numeral 16 indicates a flow control filter on the flow control filter string, reference numeral 17 indicates a packer provided in the annular space between the flow control filter string and the perforated pipe, and reference numeral 18 indicates a packer hung with the flow control filter string. A direction of arrows in the figure indicates the fluid channeling direction. As shown in FIG. 2, the fluid in the formation passes through the borehole wall and enters into the annular space between the borehole wall and the perforated pipe, so that the axial channeling is formed in the annular space between the borehole wall and the perforated pipe, and then passes through the flow control filter and enters into the flow control filter string. This axial channeling destroys the pack-off effect of the packer provided between the flow control filter string and the perforated pipe, thus a good water control effect can not be realized.